The present invention is directed to an apparatus for pelletizing a petroleum resid wherein the resid is prilled in a molten state using a rotating prilling head, liquid particles of the resid made by the prilling head are formed into spheres before solidifying, and the spherical particles are then quenched and solidified in substantially spherical shape. More particularly, the invention is directed to a prilling head assembly and a prilling vessel equipped with the assembly.
The residue from petroleum distillation has a wide number of uses, including paving asphalt and fuel. Paving grade asphalt used in road construction must meet a number of specifications, including the latest SHRP specification, viscosity (usually 200-5000 poises at 60xc2x0 F.), penetration (usually greater than 30 to 200 dmm), penetration ratio 15xc2x0 F./25xc2x0 F. (usually above about 0.3), ductility, temperature susceptibility, and others.
Contacting the petroleum resid fraction with air at an elevated temperature, also referred to as xe2x80x9cair blowing,xe2x80x9d is a conventional way to improve the characteristics of certain grades of resid to make them suitable for use as a paving; asphalt. However, the prior art does not appear to disclose the practical application of air blowing a relatively soft resid to obtain a relatively hard resid that can be pelletized for storage and/or shipment. As used in the present specification and claims, a xe2x80x9csoft reside xe2x80x9d or a xe2x80x9clow softening point temperaturexe2x80x9d refers to a petroleum residue having a penetration above 0 and Ring and Ball (RandB) softening point temperature below 200xc2x0 F. A xe2x80x9chard residxe2x80x9d or a xe2x80x9chigh softening point temperaturexe2x80x9d refers to a petroleum residue with a penetration of essentially 0 and RandB softening point temperature above 200xc2x0 F.
Representative references disclosing resid or asphaltene air blowing equipment and methodology include U.S. Pat. No. 2,616,837 to Roediger; U.S. Pat. No. 2,627,498 to Firik et al; U.S. Pat. No. 2,861,939 to Biribauer et al; U.S. Pat. No. 2,889,296 to Morris et al; U.S. Pat. No. 3,462,359 to Fauber; U.S. Pat. No. 3,598,716 to Fauber; U.S. Pat. No. 3,751,278 to Alexander; U.S. Pat. No. 3,779,892 to Forster et al; U.S. Pat. No. 3,868,315 to Forster et al; U.S. Pat. No. 3,935,093 to Senolt et al; U.S. Pat. No. 3,989,616 to Pagen et al; U.S. Pat. No. 4,052,290 to cushman et al; U.S. Pat. No. 4,207,117 to Espenscheid et al; U.S. Pat. No. 4,283,230 to Clementoni et al; U.S. Pat. No. 4,332,671 to Boyer; U.S. Pat. No. 4,933,067 to Rankel; U.S. Pat. No. 4,975,176 to Begliardi et al; U.S. Pat. No. 5,228,977 to Moran et al; U.S. Pat. No. 5,320,739 to Moran et al; U.S. Pat. No. 5,932,186 to Romine et al; and U.S. Pat. No. 5,939,474 to Gooswilligen et al. Air blowing technology is commercially available under the trade designation BITUROX, for example.
In contrast to paving asphalt, the specifications for fuel grade petroleum resid that is burned as a fuel are much less stringent. The resid generally has a higher calorific value and better combustion characteristics compared to coal and petroleum coke, which is why resid has been added to coal and coke as an additive to improve calorific value and aid combustion. However, heavy resid with a low softening point temperature is difficult to store and/or transport without significant handling and packaging requirements. Over time, even when they initially may appear to be solid at ambient conditions, these low-softening-point-materials exhibit liquid flow characteristics. These materials have typically been transported as a semi-solid product, as a neat liquid product, or as a cutback liquid product. The semi-solid form must be shipped in a closed container to prevent leakage and spillage, is usually reheated prior to use, and the high cost, of packaging and handling the material in this manner usually limits application to relatively small volumes of product.
As a neat liquid product, heavy resid is maintained at elevated temperatures sufficient to keep the material in a liquid state. This method is also expensive and has limited practical application.
As a cutback liquid product, heavy resid is mixed with light aromatic hydrocarbon cutterstocks to maintain the mixture in a liquid state at lower temperatures. As a result, the lighter hydrocarbons with which the resid is blended are substantially downgraded in value.
A pelletized resid that remains solid would be free flowing and could be readily stored, packaged, transported and handled. Previous attempts at pelletizing resid with a low softening point temperature have relied on encapsulating the resid with a solid coating. Coating the resid complicates the encapsulating process, results in a compositionally heterogeneous product, adds cost due to the generally expensive nature of the coating material, is not always effective due to rupture or breakage of the coating and/or to dissolution of the coating by water if the coating is water soluble, and the coating can adversely affect the combustion characteristics of the resid. Representative references teaching various encapsulation apparatus and methodology include U.S. Pat. No. 3,015,128 to Somerville; U.S. Pat. No. 3,310,612 to Somerville; U.S. Pat. No. 4,123,206 to Dannelly; U.S. Pat. No. 4,128,409 to Dannelly; U.S. Pat. No. 4,386,895 to Sodickson; and U.S. Pat. No. 5,637,350 to Ross.
U.S. Pat. No. 4,931,231 to Teppo et al discloses a method for manufacturing discrete pellets of asphaltic material by flowing the asphaltic material in molten form as an elongated annular stream directly into cooling water to solidify and shatter the elongated stream into discrete solid particles. The particles formed as a result of shattering are not spherical and have undesirable flow and/or handling characteristics. For example, the particles may be dust-free when made, but because of any jagged edges, might result in formation of considerable dust upon handling.
U.S. Pat. No. 3,877,918 to Cerbo discloses apparatus for producing spherical glass particles by centrifugally projecting solid crushed glass particles into the draft tube of a bead furnace using a rotary receptacle. The rotary receptacle forms a cloud of evenly dispersed solid glass particles, which are directed upwardly into the expansion chamber of the furnace to heat and shape the glass-particles by surface tension into spheres.
The prior art does not appear to disclose a method or apparatus for making spherical petroleum resid pellets by feeding the resid in a molten state to a rotating prilling head, allowing the resid discharged from the prilling head to break into particles and form into spheres due to the surface tension of the molten resid as the particles pass by gravity through a high temperature zone, and then quenching the molten material in a cooling medium to solidify the particles in their substantially spherical form. Nor does there appear to be any prior disclosure of substantially spherical, compositionally homogeneous. (uncoated) petroleum resid pellets having a high softening point temperature, nor of a method or apparatus for making spherical resid pellets for ambient temperature storage and shipment for use in combustion processes as a fuel or fuel additive.
The present invention produces substantially spherical particles from a material such, as petroleum resid that is normally solid at ambient temperature, but can be liquefied at an elevated temperature. The present invention produces a compositionally homogeneous pelletized petroleum resid product suitable for ambient-temperature storage and shipment prior to an end use. The pellets are relatively hard and have a softening point temperature above 200xc2x0 F. so that they do not stick together at ambient storage and transportation temperatures. If the resid feedstock is not sufficiently hard, it can be hardened by oxidation with air at elevated temperature. The resid is prilled at molten temperatures using a rotating prilling head that discharges the molten resid into a high temperature vapor space. As the resid is thrown away from the prilling head and falls by gravity, it breaks into small pieces that form into spheres while liquid. After the spheres are formed in a liquid state, the pellets are cooled and solidified, for example, by passing the spheres through a water mist and collecting them in a water bath.
Broadly, the invention provides a process for pelletizing a petroleum resid. The process comprises (1) heating the resid to a temperature at which it is in a liquid state, (2) continuously feeding the molten resid to an inlet of a centrifugal prilling head comprising a plurality of radially arrayed discharge orifices in fluid communication with, the inlet, (3) rotating the prilling head to discharge the resid from the orifices into free space near an upper end of a pelletizing vessel having a diameter larger than a throw-away diameter of the discharged resid, (4) allowing the discharged resid to break apart and form into substantially spherical pellets in a high temperature zone of the pelletizing vessel at which the resid is liquid, and to fall downwardly into contact with a cooling medium in which the resid is insoluble and which is maintained at a temperature effective to cool/solidify the pellets, (5) withdrawing a mixture of the solidified pellets and the cooling medium from the pelletizing vessel, and (6) substantially separating the pellets from the cooling medium.
The invention also provides a prilling head assembly for a vessel for pelletizing a petroleum resid. The prilling head assembly is preferably mountable on the upper end of a pelletizing vessel for throwing feed material radially outward into an upper prilling zone in the vessel. The assembly includes: (1) a rotary union including a housing, a feed inlet, a rotatable pipe depending from the housing, a flow path between the feed inlet and an upper end of the rotatable pipe disposed within the housing, and a fluid tight seal between an exterior surface of the pipe and an opening in the housing; (2) a lower end of the rotatable pipe connected to a prilling head having a flow passage in fluid communication between an outlet from the-lower end of the rotatable pipe and a plurality of orifices radially offset from an axis of the rotatable pipe; (3) a support housing having a mount for attachment to the pelletizing vessel and upper and lower bearings adjacent respective upper and lower ends of the support housing for rotatably receiving the rotatable pipe; and (4) a drive wheel secured to the rotatable pipe. Preferably, the prilling head assembly further comprises a detachable coupling on the rotatable pipe between the rotary union and the upper bearing. The upper bearing is preferably mounted to the top flange, and the lower bearing to a lower bearing mount flange.
The mount in the prilling head assembly preferably includes a mounting flange and the support housing includes a fixed pipe with a larger inside diameter than the outside diameter of the rotatable pipe. The fixed pipe depends from the mounting flange. The prilling head assembly preferably includes a lower dust seal at a lower end of the fixed pipe adjacent an opening in a lower end panel located between the lower bearing and the prilling head, and an upper dust seal adjacent an opening in the mounting flange receiving the rotatable pipe. The support housing preferably includes a port for introducing inert gas into the annulus between the fixed pipe and the rotatable pipe.
The support housing preferably includes a top flange secured by a bracket in spaced. relation above the mounting flange. The upper bearing is secured to the top flange. The drive wheel can be conveniently disposed between the top flange and the mounting flange. The discharge orifices in the prilling head are preferably arrayed at a circumference of the prilling head in a plurality of vertically spaced upper and lower rows. The lower row or rows can be disposed at a smaller diameter from the axis of rotation of the prilling head than the upper row or rows. The prilling head preferably has a circumference tapered from an uppermost row of orifices to a lowermost row, and can be rotated at from about 100 to about 5000 rpm. The prilling head preferably has a diameter from about 2 inches to about 5 feet, the orifices a diameter from about {fraction (1/32)}-inch to about 1 inch and a production capacity of from about 1 to about 1000 lbs/hr of resid per orifice, the throw-away diameter from about 1 foot to about 15 feet, and the pellets a size range from about 0.1 mm to about 10 mm.
The cooling medium is preferably water, and the water bath is maintained in the pelletizing vessel at a temperature from about 40xc2x0 to about 190xc2x0 F. The water is preferably introduced into the pelletizing vessel as an inwardly directed spray, e.g. a fine mist, in a cooling zone above the bath to-at least partially cool the spherical pellets before they enter the bath. The slurry withdrawn from the pelletizing vessel is preferably no more than about 50xc2x0 F. warmer than the water introduced into the cooling zone. The process can also include the steps of collecting water from the separation step, and filtering, cooling, and recirculating the cooled water to the cooling zone.
The process can also include the step of venting vapor near an upper end of the pelletizing vessel and/or the step of heating an upper end of the pelletizing vessel to maintain a substantially constant temperature zone in the vicinity of the prilling head. The process can further comprise the step of transporting the recovered pellets at ambient temperature to a location remote from the pelletization vessel where the pellets are used for combustion, as a combustion improver or additive to coke and/or coal, in admixture with a cutterstock for fuel oil, or the like.
The petroleum resid fed to the heating step preferably has a penetration of essentially 0 and a softening point temperature from 200xc2x0 to 400xc2x0 F., more preferably having a-softening point temperature from about 230xc2x0 to about 350xc2x0 F. The resid is preferably obtained as the asphaltene-rich fraction from a solvent deasphalting process. The resid feed is preferably heated to a temperature from about 350xc2x0 to about 700xc2x0 F., and the pellets recovered from the separation can have a residual water content of from 0.1 to 10 weight percent. The process can also include burning the transported resid pellets, for example, as a combustion fuel, as an additive in the combustion of coal and/or petroleum coke or as a blend component with cutterstock in a fuel oil.
The process can further comprise the step of contacting a soft petroleum resid with air at a temperature from about 350xc2x0 to about 700xc2x0 F. for a period of time effective to reduce the penetration of the resid to essentially 0 and increase the softening point temperature to above 200xc2x0 F. to form a hard resid suitable for use as the resid feed in the heating step. The soft resid can be obtained as atmospheric tower resid or the asphaltene-rich fraction from solvent deasphalting of a petroleum residue, especially propane deasphalting. The air-contacting step is preferably for a period of time from about 2 to about 5 hours.
In another aspect of the invention, there is provided a process for making petroleum resid pellets from a soft petroleum resid. The process includes contacting a soft resid having a penetration greater than 0 and a softening point temperature below about 200xc2x0 F. with air at a temperature from about 350xc2x0 to about 700xc2x0 F. for a period of time effective to form a hard resid having a penetration of essentially 0 and a softening point temperature above 200xc2x0 F., and forming the hard resid into pellets. The process can also include burning the pellets as a fuel or fuel additive, for example.
In a further aspect of the invention, there is provided a pelletizer for making spherical pellets from a material such as petroleum resid which is normally solid at ambient temperature, but which can be liquefied at elevated temperature. The pelletizer includes an upright pelletizing vessel having an upper prilling zone, a hot sphere-forming zone below the prilling zone, a cooling zone below the sphere-forming zone, and a lower liquid cooling bath below the cooling zone. A prilling head is centrally disposed in the prilling zone, and is rotatable along a vertical axis. The prilling head has a plurality of discharge orifices for throwing the molten materially radially outwardly. A throw-away diameter of the prilling head is less than an inside diameter of the pelletizing vessel. A process line is provided for supplying the material to the prilling head. A vertical height of the sphere-forming zone is sufficient to allow liquid material discharged from the prilling head to form into a substantially spherical shape while in the liquid state. Nozzles can be provided for spraying liquid cooling medium, preferably water in the form of a mist, inwardly into the cooling zone to cool and solidify at least an outer surface of the spheres to be collected in the bath. Another line is provided for supplying water to the nozzles and the bath to maintain the relatively low temperature of the bath in the pelletizing vessel. A further line is provided for withdrawing a slurry of the pellets in the bath water. A liquid-solid separator is provided for dewatering the pellets from the slurry.
The pelletizer can also include an oxidation vessel for contacting a soft resid, having a penetration greater than 0, and preferably less than 100 dmm, with air at a temperature from about 350xc2x0 to about 700xc2x0 F. for a period of time effective to reduce the penetration of the resid to essentially 0 and to increase the softening point temperature to above 200xc2x0 F. to form a hard resid suitable for feed to the prilling head. The pelletizer can preferably further include a solvent deasphalting unit for obtaining the soft resid as the asphaltene fraction from solvent de-asphalting of a petroleum residue.
The discharge orifices of the prilling head are preferably arrayed at a circumference of the prilling head in a plurality of vertically spaced upper and lower rows wherein the lower row or rows are disposed at a smaller diameter from the axis of rotation of the prilling head than the upper row or rows. The prilling head can have a circumference tapered, either continuously or stepped, from an uppermost row at a relatively large diameter to a lowermost row at a relatively small diameter. In one alternative embodiment, the prilling head preferably comprises a plurality of rings of different diameter with orifices formed in an outer circumference of each ring, wherein the rings are secured to the prilling head in a descending fashion, each successively lower ring having a smaller diameter than the preceding ring. The pelletizer preferably has a drive for rotating the prilling head at from about 100 to about 5000 rpm wherein the prilling head has a diameter from about 2 inches to about 5 feet, and wherein the orifices have a diameter from about {fraction (1/32)}-inch to about 1-inch and a production capacity of from about 1 to about 1000 lbs/hr of molten material per orifice.
The cooling medium is preferably water and the pelletizer also preferably includes a cooler for maintaining the bath in the pelletizing vessel at a temperature from about 600 to about 190xc2x0 F. The aqueous bath preferably contains a minor amount of a non-foaming surfactant. The vessel preferably has a conical bottom containing the bath and a discharge at a lower end of the conical bottom for feeding the slurry into the withdrawal line. A filter can be provided for filtering water recovered from the liquid-solid separator, a cooler provided for cooling the filtered water and a recirculation line provided for recirculating the cooled water to the supply line.
A vent line is preferably provided for withdrawing vapor from the pelletizing vessel near an upper end thereof. A heater can also be provided for heating an upper end of the vessel to maintain a substantially constant temperature zone adjacent the prilling head, particularly during startup operations. In one preferred embodiment, a line is provided for introducing steam into the sphere-forming zone.
The liquid-solid separator preferably comprises a vibrating screen. The pelletizer can further comprise a conveyor belt for transporting the pellets from the vibrating screen to ambient temperature storage, packaging and/or shipment.
In another aspect, the present invention provides substantially spherical, homogeneous petroleum resid pellets suitable for combustion having a size range between 0.1 and 10 mm, a penetration of essentially 0, a softening point temperature from about 200xc2x0 to about 400xc2x0 F., preferably from about 230xc2x0 to about 350xc2x0 F., a residual water content of from 0.1 to 10 weight percent, and a sulfur content less than 10 weight percent. The resid pellets can comprise a hard resid produced by a process comprising contacting a soft resid with air at an elevated temperature for a period of time effective to convert the soft resid to hard resid, preferably from 2 to 5 hours.